1. Field of the Invention
The invention is directed to a piston-cylinder unit of the type wherein the piston separates the cylinder into two work chambers which communicate via a bypass groove in the cylinder depending on piston stroke position.
2. Description of the Related Art
xe2x80x9cMotor Vehicle Shock Absorber [Kraftfahrzeugstoxcex2dxc3xa4mper]xe2x80x9d, Bibliothek der Technik, Vol. 185, Verlag Moderne Industrie, pages 38 to 41, discloses a piston-cylinder unit which has a stroke-dependent damping based on at least one bypass groove in the cylinder. This proven method of stroke-dependent damping has the disadvantage that vehicles with different empty weights, e.g., because of differences in their outfitting, cannot make use of a part of the bypass groove and, therefore, cannot make use of a region of the comfortable stroke position of the shock absorber. It is endeavored, when the vehicle is stationary, to move the piston out as centrally as possible within the bypass groove. In vehicles with leveling control, this task is taken on by a supply system which raises or lowers the vehicle body in relation to the vehicle axis. A leveling control cannot be used for many vehicles and applications, for example, because of excessive technical expenditure.
It is the object of the present invention to provide a piston-cylinder unit with at least one bypass groove between the work spaces in which the problem known from the prior art is overcome.
According to the invention, this object is met in that the cylinder is formed of multiple parts and a portion of the cylinder with the at least one bypass groove is displaceable axially relative to at least one further portion of the cylinder.
With this very simple method, the bypass groove can be displaced within limits independent from a normal position of the piston without great expenditure. Accordingly, in a vibration damper in a vehicle, the bypass groove can be adapted to the normal position of the vehicle when the vehicle is stationary.
However, application is not restricted only to vibration dampers. Bypass grooves are often used in air springs, e.g., as employed in vehicle flaps, and correspond to an opening angle of the vehicle flaps. When the bypass groove is displaced, the opening angle also changes.
In a further construction, the cylinder has a first portion which is guided coaxially inside a second portion.
The second portion of the cylinder advantageously has a base and the first portion carries a piston rod guide for a piston rod.
In order to ensure a continuous adjustment of the position of the bypass groove, the two portions of the cylinder are connected with one another via a thread.
The two portions of the cylinder are clamped via a retaining screw for operating reliability.
According to a feature of the invention, the first portion and the second portion of the cylinder overlap or cover one another, at least one seal being arranged in this area.
Further, the second portion of the cylinder has an adjusting length area having a fastening thread for the retaining screw.
In an application of a vibration damper indicated by way of example, it is possible that an axially movable dividing or separating piston which separates a work space from a compensation space is arranged inside the second portion of the cylinder. Accordingly, there is a larger cross-sectional surface available for the separating piston, so that a gas pressure in the compensation space can be comparatively small.
In another construction, the portions of the cylinder which are displaceable relative to one another have at least one axial projection and a recess or cutout in the direction of the longitudinal axis of the piston-cylinder unit which engage one inside the other, the length of the at least one bypass groove being changeable with the position of the projection within the cutout.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.